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Porcine Reproductive and Respiratory Syndrome (PRRS)

Introduction

Porcine Reproductive and Respiratory Syndrome (PRRS) is a highly important viral disease of pigs characterized by reproductive failure in breeding stock and respiratory disease in growing pigs. It is one of the most economically significant diseases in the global swine industry due to production losses, increased mortality, and long-term herd instability.

Etiology
Causative Agent

PRRS is caused by Porcine Reproductive and Respiratory Syndrome Virus (PRRSV), a member of the genus Arterivirus, family Arteriviridae.

Virus Characteristics
  • Enveloped, single-stranded positive-sense RNA virus
  • High genetic variability and frequent mutation
  • Two major types: PRRSV-1 (European type) and PRRSV-2 (North American type)
  • Moderately fragile in the environment but stable in organic material
Epidemiology
Species Affected
  • Domestic pigs (primary host)
  • Wild boar (reservoir in some regions)
Transmission
  • Direct contact with infected pigs
  • Aerosol transmission over short distances
  • Semen (important route in breeding herds)
  • Transplacental infection (from sow to fetus)
  • Fomites (equipment, clothing, vehicles)
Risk Factors
  • Introduction of infected or carrier animals
  • Poor biosecurity
  • High-density pig production systems
  • Movement of contaminated semen
Pathogenesis
Initial Infection

The virus enters via respiratory or reproductive routes and targets macrophages, particularly pulmonary alveolar macrophages.

Immune Suppression
  • Impaired macrophage function
  • Reduced ability to clear secondary infections
Viremia and Spread
  • Systemic spread via bloodstream
  • Infection of lymphoid tissues and reproductive organs
Fetal Infection
  • Transplacental infection leads to abortion, stillbirth, or weak piglets
  • High mortality in neonatal piglets
Clinical Signs
Reproductive Form
  • Late-term abortions
  • Stillborn piglets
  • Mummified fetuses
  • Weak-born piglets with high pre-weaning mortality
  • Reduced conception rates
Respiratory Form
  • Coughing
  • Dyspnea
  • Fever
  • Reduced growth rates in growing pigs
Systemic Signs
  • Depression
  • Anorexia
  • Increased susceptibility to secondary infections (especially bacterial pneumonia)
Summary for Practitioners

PRRS should be suspected in herds with reproductive failure and chronic respiratory disease, especially when accompanied by poor growth performance and secondary bacterial infections.

Postmortem Findings
Gross Lesions
  • Interstital pneumonia (“meaty lungs” appearance)
  • Lymph node enlargement
  • Fetal lesions: autolysis, mummification, or no obvious lesions
Microscopic Lesions
  • Interstitial pneumonia
  • Lymphoid hyperplasia or depletion
  • Macrophage infection in lung tissue
Diagnosis
Clinical Diagnosis

Based on reproductive failure, respiratory disease, and herd history.

Laboratory Diagnosis
  • RT-PCR for viral RNA detection
  • Serology (ELISA)
  • Virus isolation
Differential Diagnosis
  • Classical swine fever (CSF)
  • African swine fever (ASF)
  • Swine influenza
  • Mycoplasma hyopneumoniae infection
  • Porcine circovirus type 2 (PCV2)
Summary for Practitioners

Diagnosis often requires laboratory confirmation due to similarity with other respiratory and reproductive diseases of pigs.

Treatment
General Approach

No specific antiviral treatment is available for PRRS.

Supportive Care
  • Antibiotics for secondary bacterial infections
  • Anti-inflammatory drugs
  • Improved nutrition and management
Summary for Practitioners

Treatment is supportive. Control focuses on reducing secondary infections and improving herd immunity.

Control and Prevention
Biosecurity
  • Strict control of animal movement
  • Quarantine of incoming pigs
  • Semen testing and control programs
Vaccination
  • Modified live and inactivated vaccines available
  • Used to reduce clinical severity and viral spread
Herd Management
  • All-in/all-out systems
  • Depopulation-repopulation strategies in severe cases
  • Continuous monitoring of herd status
Summary for Practitioners

Effective control requires integrated strategies including vaccination, strict biosecurity, and herd management adjustments.

Zoonotic Importance

PRRS is not zoonotic and does not infect humans.

Economic Importance

PRRS causes major economic losses due to reproductive failure, piglet mortality, poor growth performance, increased medication costs, and long-term herd instability.

Summary

Porcine Reproductive and Respiratory Syndrome is a highly significant viral disease of pigs affecting both reproductive and respiratory systems. Control is challenging due to viral variability and persistence, requiring integrated herd health management strategies.